The purpose of this research is to investigate preliminary evidence of a suppression of the rod system by the cone system of the human retina, to clarify the role of receptor orientation in the Stiles-Crawford effect, and to analyze two new components of the transient Stiles-Crawford effect: a transient loss of acuity, and transient gradients of brightness and sensitivity withim a homogeneously illuminated region of the retina. All observations will be based on psychophysical methods.